Leitch Pass-Through Implementation Notes

Leitch Pass-Through protocol for router control is supported in Helm, RouteMaster and RouteMaster VR.

Originally developed by Leitch Technology in 1999, the protocol is used by Harris and Imagine Communications routers. Other manufacturers like For-A also use variants of the protocol, with custom extensions. Modern Harris/Imaging routers use the more extensive Harris LRC protocol.

RouteMaster uses the protocol for both outgoing and incoming connections, allowing third-party systems using Pass-Through to control RouteMaster.  Helm uses it for outgoing connections to control routers.


The standard Pass-Through protocol does not give access to mnemonics for router sources and destinations. Also, there is no way to query the Lock status of a destination.

Use over TCP/IP

Originally designed as an RS-422 serial protocol, Pass-Through can also be used over TCP/IP. There is no standard port number for this.

Supported and Required Commands

This table details the commands used for outgoing connections, and the commands supported for incoming connections.

Command Outgoing Incoming Notes
Enable Reporting Yes RouteMaster always has reporting enabled
Request Level Status Yes Yes
Crosspoint Take Yes Yes
Lock/Protect/Unlock Yes Yes
Crosspoint Status Yes Yes

Special Properties

For outgoing connections, the following properties can be set directly in Helm Designer, or in the RouteMaster configuration file.

Username string Name of user to log in. If blank, no authentication is attempted
Password string Password for login
LoginDelay milliseconds Delay used before sending Username and Password at login. Default = 1000
ID integer ID to use for Panel Take and Lock/Unlock commands. Default is zero.